Solenoid valves are relatively simple devices that can show up in areas outside industrial applications. For instance, if you listen to your dishwasher, then you might hear its solenoid valve opening and closing during the washing process.
What is a solenoid valve?
A solenoid valve converts an electromagnetic signal into a mechanical movement and is usually used to open and close valves digitally. It consists of a wire with an iron plunger in the middle, with a short movement range into the coil.
When sending energy to the coil, the magnetic field created will force the plunger to move to the middle of the coil. When the magnetic energy subsides, the plunger moves back to its natural position.
Solenoid valve applications
First, the pneumatic control valve positioner has an air supply to make everything work, including the valve actuator. You have an instrument input, with a range of 3 to 15 pounds per square inch (psi), and the air output to move the valve actuator.
Many pneumatic devices use a nozzle and flapper system to give a variation in the compressed air signal. It can be considered as made up of two parts—the actuator and the valve. In the arrangement a flexible diaphragm forms a pressure tight chamber in the upper half of the actuator and the controller signal is fed in.
Movement of the diaphragm results in a movement of the valve spindle and the valve. The diaphragm movement is opposed by a spring and is usually arranged so that the variation of controller output corresponds to full travel of the valve.
The valve body is arranged to fit into the particular pipeline and houses the valve and seat assembly. Valve operation may be direct acting where increasing pressure on the diaphragm closes the valve.
A reverse acting valve opens as pressure on the diaphragm increases. The diaphragm movement is opposed by a spring which will close or open the valve in the event of air supply failure depending upon the action of the valve.
You can apply a solenoid in a control valve system in two ways. If you have a valve that works only in on/off conditions, then you can have a three-way solenoid valve to apply and release pressure to the actuator when necessary.
The second application is for safety. A three-way solenoid valve installed between the positioner and the valve actuator can control the valve if a failure happens, either keeping it in one position or moving it faster.
If you want to learn more about solenoid valves, you can watch this video: